Ring Grit Remover

ABSTRACT

A grit removal unit for a wastewater system including a grit removal chamber with a substantially annular vertical wall. A horizontal annular ring above the chamber bottom extends inwardly from the annular vertical wall, with an influent channel extending into the chamber beneath the ring and an effluent channel above the rim and extending out of the chamber. The influent and effluent channels both have inner side walls with a curved portion, with both curved portions extending through an arc of at least 90 degrees within the chamber annular vertical wall.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S.Provisional Application Ser. No. 62/035,594, filed Aug. 11, 2014 andU.S. Ser. No. 14/823,488, filed Aug. 11, 2015, which are herebyincorporated by reference in their entirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

MICROFICHE/COPYRIGHT REFERENCE

Not Applicable.

FIELD OF THE INVENTION

The present invention relates to a grit selector or trap for selectivelyremoving sand and grit from a flowing stream of fluid.

BACKGROUND OF THE INVENTION

Grit is one of the most unpredictable and difficult materials a sewagetreatment plant must handle. Grit can be defined as the heavy mineralmatter present in sewage. It is principally made up of sand, gravel, andinorganic material which reaches a sewage disposal plant. It is desirousto remove this material as it cannot be treated, reduced in size, oreliminated by biological treatment methods. It presents a problem towaste treatment as it is hard and abrasive. It wears pumps and othermechanical devices. It is heavy and accumulates in clarifiers, treatmentbasins, digesters, etc., where it must sometimes be removed by manually.

Grit removal devices of various designs have been proposed to removegrit from a flowing stream of water. Several such devices are shown, forexample, in U.S. Pat. Nos. 3,941,698, 4,107,038, 4,519,907, 6,811,697,6,881,350, and 8,906,233.

U.S. Pat. No. 3,941,698 includes an upper settling chamber and a lowergrit storage chamber. The settling chamber, being of large diameter,communicates with the storage chamber through a relatively small openingin a substantially flat transition surface therebetween. Rotatingpaddles positioned within the settling chamber, a short distance abovethe transition surface, can enhance the natural rotational flow ofliquid entering the settling chamber adjacent the outer periphery torotate about the chamber as a forced vortex resulting in an upwardspiral flow which urges the settled particles across the transitionsurface towards the opening. The heavier settled particles fall throughthe opening into the storage chamber and the lighter organic particlesrise in the spiral flow. The contents in the storage chamber are lightlyair scoured prior to removal to cause any organics therein to be liftedout of the storage chamber and returned to the settling chamber.

A similar type of grit removal device is disclosed in U.S. Pat. No.4,107,038, in which a ramp is in communication with the flume portion ofthe inlet trough to cause grit to follow the ramp down towards thetransition surface. A baffle is also positioned in the settling chamberagainst which the rotating liquid impinges to deflect the liquiddownwardly into a generally toroidal flow pattern that spirals aroundthe periphery of the settling chamber. The toroidal motion of the liquidmoves the grit on the transition surface towards the center opening.

The above-described prior art devices operate on the forced vortexprinciple. In these devices the head at the periphery of the settlingchamber is higher than at the center of the settling chamber. Thiscauses liquid to flow down the wall of the settling chamber to thebottom thereof and across the bottom to the point of lower head at thecenter thereof. It is this transverse circulatory flow pattern whichpermits the device to work. The particulate matter in suspension mustfollow this path to reach the bottom of the settling chamber and becarried to the center of the transition surface to the storage chamber.This takes some time and some of the particulate matter may not travelthe full circuit before it is caught in the flow passing out theeffluent, which results in a lowering of grit removal efficiency.

In still other grit removal devices such as shown in U.S. Pat. Nos.4,767,532, 6,811,697, and 8,906,233 flow toward the center of a chamberis facilitated by a rotating propeller or paddle. U.S. Pat. No.8,906,233 also includes a ring around the interior periphery of thesettling chamber blocking fluid flowing around the outside of thechamber from rising up to the level of the chamber outlet.

Grit removal devices as described above, whether operating by settlingor vortex action, require a relatively large footprint, presenting spaceproblems in designing overall treatment facilities in which the gritremoval devices are only a part. Of course, larger devices areinherently more costly, and can use more energy. Further, such devicesare not as well adapted as might be desired to operate efficiently inenvironments in which the flow rate varies widely. Still further, theability of the devices to efficiently remove grit can always beimproved.

The present invention is directed toward, inter alia, one or more of theproblems set forth above.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a grit removal unit for awastewater system is provided, including a round grit removal chamberdefined by a bottom surface and a substantially annular vertical wallextending up from the bottom surface, a substantially horizontal annularring spaced above the chamber bottom surface and extending inwardly fromthe chamber annular vertical wall to an inner edge, and an enclosedinfluent channel extending into the chamber beneath the ring. Theinfluent channel has an outer side wall with a planar portion tangent tothe chamber vertical wall and an inner side wall with a planar portionand a curved portion extending through an arc of at least about 90degrees within the chamber annular vertical wall.

In one form of this aspect of the invention, the inner side wall is aJ-shaped baffle having a leg with a curved portion extending at least 90degrees and concentric with the chamber annular vertical wall, thecurved portion secured around the inner diameter of the ring. In analternate form, the inner side wall curved portion spirals from aproximate end adjacent the baffle leg to a distal end spaced from thebaffle leg, the spiral having a radius at the distal end which is lessthan the radius at the proximate end.

In another form of this aspect of the invention, the enclosed influentchannel inner side wall curved portion extends through an arc of betweenabout 90 degrees to about 270 degrees within the chamber annular wall.

In another aspect of the present invention, a grit removal unit for awastewater system is provided, including a round grit removal chamberdefined by a bottom surface and a substantially annular vertical wallextending up from the bottom surface, a substantially horizontal annularring spaced above the chamber bottom surface and extending inwardly fromthe chamber annular vertical wall to an inner edge, an enclosed influentchannel extending into the chamber beneath the ring, and an effluentchannel above the rim and extending out of the chamber. The influentchannel has an outer side wall with a planar portion tangent to thechamber vertical wall and an inner side wall with a planar portion and acurved portion extending through an arc of at least 90 degrees withinthe chamber annular vertical wall. The effluent channel has an outerside wall with a planar portion tangent to the chamber vertical wall andan inner side wall with a planar portion and a curved portion extendingthrough an arc of at least 90 degrees within the chamber annularvertical wall.

In one form of this aspect of the invention, the influent channel has anoutlet substantially aligned with an inlet to the effluent channel so asto substantially prevent influent from the influent channel outlet fromexiting to the effluent channel input without first entirely circlingthe chamber.

In another form of this aspect of the invention, the influent channeloutlet is substantially aligned with and below the effluent channelinlet.

In still another form of this aspect of the invention, the enclosedinfluent channel inner side wall curved portion and the effluent channelinner side wall both extend through an arc of between about 90 degreesto about 270 degrees within the chamber annular wall.

In yet another form of this aspect of the invention, the enclosedinfluent channel inner side wall curved portion and the effluent channelinner side wall curved portion both extend through an arc of about 180degrees.

In another form of this aspect of the invention, the radially innersides of the influent and effluent channels are defined by J-shapedbaffles with curved portions substantially concentric with the chamberannular vertical wall.

In still another form of this aspect of the invention, the inner sidewall curved portion spirals from a proximate end adjacent the baffle legto a distal end spaced from the baffle leg. In a further form, thespiral has a radius at the distal end which is less than the radius atthe proximate end.

In still another aspect of the present invention, a grit removal unitfor a wastewater system is provided, including a round grit removalchamber defined by a bottom surface and a substantially annular verticalwall extending up from the bottom surface, a substantially horizontalannular ring extending inwardly from the chamber annular vertical wallto an inner edge having a radius R_(i), the ring being spaced above thechamber bottom surface, an influent channel through an opening in thechamber vertical wall beneath the ring, and an effluent channel throughan opening in the chamber vertical wall above the ring. The influentchannel has one influent side wall substantially tangential to thechamber vertical wall at the influent channel opening in the chambervertical wall, and a influent inner side wall having a substantiallyflat portion parallel to the one influent side wall and a curved portionextending between the chamber bottom surface and the ring, the influentinner side wall curved portion having a radius R_(i) and extendingthrough an arc of at least 90 degrees, the influent channel having itsoutlet at the end of the influent inner side wall curved portion. Theeffluent channel has one effluent side wall substantially tangential tothe chamber vertical wall at the effluent channel opening in the chambervertical wall, and an effluent inner side wall having a substantiallyflat portion parallel to the one effluent side wall and a curved portionextending upwardly from the ring, the effluent inner side wall curvedportion having a radius R_(i) and extending through an arc of at least90 degrees, the effluent channel having its inlet at the end of theeffluent inner side wall curved portion.

In one form of this aspect of the invention, the influent channel outletand the effluent channel inlet are aligned so as to substantiallyprevent influent from the influent channel from exiting to the effluentchannel input without first entirely circling the chamber.

In another form of this aspect of the invention, the end of the influentinner side wall curved portion is substantially aligned with and belowthe end of the effluent inner side wall curved portion.

In still another form of this aspect of the invention, the influentinner side wall curved portion and the effluent inner side wall curvedportion both extend through an arc of between about 90 degrees and about270 degrees within the chamber annular wall.

In yet another form of this aspect of the invention, the inner side wallis a J-shaped baffle having a leg with a curved portion extendingthrough an angle at least 90 degrees and concentric with the chamberannular vertical wall, the curved portion secured around the innerdiameter of the ring. In a further form, the inner side wall curvedportion spirals from a proximate end adjacent the baffle leg to a distalend spaced from the baffle leg, the spiral having a radius at the distalend which is less than the radius at the proximate end.

In still another aspect of the present invention, a grit removal unitfor a wastewater system is provided, including a round grit removalchamber defined by a bottom surface and a vertical wall substantiallyannular vertical wall about a center and extending up from the bottomsurface, a substantially horizontal annular ring extending inwardly aradial distance R_(d) from the chamber annular vertical wall, the ringbeing above the chamber bottom surface, an influent channel through anopening in the chamber vertical wall and beneath the ring, and aneffluent channel through an opening in the chamber vertical wall andabove the ring. The chamber vertical wall has a radius of R_(VW) arounda chamber center. The influent channel has one influent side wallsubstantially tangential to the chamber vertical wall at the influentchannel opening in the chamber vertical wall, a second influent sidewall substantially parallel to the one influent side wall and spacedfrom the one influent side wall by the distance R_(d), and a curvedextension of the second influent side wall within the chamber, where thecurved extension has a radius of R_(ex) and R_(ex)=R_(VW)−R_(d). Thesecond influent side wall and curved extension extend from the chamberbottom surface to the ring so that the influent channel is definedbetween the first and second influent side walls, the curved extension,the ring, and the chamber bottom surface. The effluent channel has oneeffluent side wall substantially tangential to the chamber vertical wallat the effluent channel opening in the chamber vertical wall, a secondeffluent side wall substantially parallel to the one effluent side wall,and a curved extension of the second effluent side wall within thechamber. The effluent curved extension has a radius of R_(ex), whereinthe second effluent side wall and curved extension extend upwardly fromthe ring so that the effluent channel is defined above the ring betweenthe first and second effluent side walls and the curved extension. Thecurved extensions of the influent and effluent channel second side wallsextend through an arc of at least about 90 degrees around the center.

In one form of this aspect of the present invention, the output from theinfluent channel and the input to the effluent channel are aligned so asto substantially prevent influent from the influent channel from exitingdirectly to the effluent channel input without first substantiallyentirely circling the chamber.

In another form of this aspect of the invention, the end of the curvedextension of the second influent side wall is substantially aligned withthe end of the curved extension of the second effluent side wall.

In still another form of this aspect of the invention, the influentcurved extension and the effluent curved extension both extend throughan arc of about 90 degrees to about 270 degrees around the chambercenter and within the chamber annular wall.

Other objects, features, and advantages of the invention will becomeapparent from a review of the entire specification, including theappended claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a grit removal apparatus having at leastone of the advantageous new features of the present invention;

FIG. 2 is a partial cut away view of the apparatus of FIG. 1;

FIG. 3 is a second perspective view of the apparatus of FIG. 1;

FIG. 4 is a third perspective view of the apparatus of FIG. 1;

FIG. 5 is a perspective view of baffles which may advantageously definethe inner walls of the influent and influent channels according to thepresent invention;

and

FIGS. 6 and 7 are perspective views of grit removal apparatuses havingdifferent orientations of the influent and effluent channels than theorientation of the FIGS. 1-4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The Figures show an apparatus 10 for separating grit from incomingliquid sewage (influent) in accordance with the present invention. Acircular cylindrical separation chamber or basin 12 having an annularvertical side wall 13 is disposed immediately above and concentric witha cylindrical grit storage chamber 14 (see FIG. 2) of a lesser diameter.

A substantially flat transition bottom surface or floor 16 including aremovable plate 18 centered in the separation chamber 12 separates thestorage and separation chambers 14, 12. Suitable openings 19 through theplate 18 permit communication between the chambers 12, 14.

A multi-bladed propeller 20 may be mounted on a cylindrical shaft 24 forrotation, with the upper portion of the shaft 24 connected, for example,to a suitable drive 30 for rotating the propeller 20. Suchconfigurations are shown, for example, in U.S. Pat. Nos. 4,107,038,4,767,532 and 8,906,233, the disclosures of which are herebyincorporated by reference. Still other propeller and storage chamberconstructions may also be used within the scope of some aspects of thepresent invention as described herein.

An influent channel or inlet trough 40 has a covered downwardlyextending influent flume portion 42 to introduce an influent liquidstream directly into a lower portion (i.e., the bottom) of theseparation chamber 12 through an opening at the bottom of the separationchamber annular side wall 13. The flume portion 42 includes a ramp atits bottom which may be advantageously sloped at, for example, about 20degrees, with the ramp and the ceiling of the flume portion 42 beingsubstantially parallel.

The influent channel 40 also has an outer side wall 46 which issubstantially tangential to the separation chamber annular side wall 13on one side of the bottom chamber opening and an inner side wall orbaffle 48 described in greater detail hereafter.

An annular, ring-shaped flange or ring 50 is secured or married aroundthe separation chamber annular side wall 13 at a height above thechamber floor 16 which is substantially equal to the vertical height atthe bottom end of the flume portion 42 and the vertical height of thebottom of an effluent channel or outlet trough 60 through an opening atthe top of the separation chamber annular side wall 13. The ring 50 thushas an outer diameter equal to the radius of the vertical wall of theseparation chamber 12 (R_(vw)) and a radial dimension (R_(d)), and aninner edge having an inner radius (R_(i)), where R_(vw)−R_(d)=R_(i). Thering 50 may advantageously extend around the entirety of the separationchamber 12, although it should be appreciated that a ring 50 of lessthan 360 degrees could also be advantageously used in some aspects ofthe present invention.

It should be noted that the annular components as described herein arecurved around a center 62 which is generally aligned with thecylindrical shaft 24 of the propeller 20.

The effluent channel 60 allows fluid to flow out of the separationchamber 12 through an opening at the top of the separation chamberannular side wall 13. The effluent channel 60 also has an outer sidewall 64 which is substantially tangential to the separation chamberannular side wall 13 on one side of the top chamber opening and an innerside wall or baffle 68 described in greater detail hereafter.

Specifically, the inner side walls 48, 68 may be advantageously definedby bottom and top J-shaped vertical baffles 70, 72 secured to the ring50, wherein each includes a straight portion 80, 82 and a curved portion90, 92, wherein the curved portion 90, 92 may advantageously be securedto the inner edge of the ring 50. In one aspect of the presentinvention, the straight portions 80, 82 are substantially parallel tothe respective outer side walls 46, 64, spaced therefrom by a distanceof about R_(d). The curved portions 90, 92 may be substantiallyconcentric with the cylindrical separation chamber outer wall 13, with adiameter less than the chamber outer wall 13 of about R_(d).

It should be understood, however, that the curved portions 90, 92 mayalternatively not be substantially concentric with the cylindricalseparation chamber outer wall 13, with the radius at a given point on anarc (R_(A)) being a function of the arcuate position (Θ) at that point,or R_(A)=f(Θ), For example, the curve of the curved portions 90, 92could spiral in the direction of flow with the radius of curvaturedecreasing in the direction of flow.

The bottom J-shaped baffle 70 extends up from the chamber floor 16 tothe ring 50, so that the influent channel 40 is enclosed on top andbottom by the ring 50 and floor 16 and on opposite sides by the outerside wall 46 and inner side wall (baffle) 48. The top J-shaped baffle 72extends up from the ring 50, so that the effluent channel 60 is on topof the ring 50 and between the chamber outer side wall 46 and inner sidewall (baffle) 68.

Advantageously the curved portions 90, 92 of the J-shaped baffles 70, 72extend through an arc of at least about 90 degrees and up to about 270degrees (i.e., plus or minus 10 degrees).

It should be appreciated that extending the bottom baffle 70 through anarc inside the separation chamber 12 will ensure that the influent willall flow through at least that arc without exiting into the chamber 12,and without entering the effluent channel 60. Moreover, when the curvedportion 90 of the bottom J-shaped baffle 70 extends through an arc of,for example, 180 degrees, it should be recognized that as flow of thatinfluent continues around the chamber 12, it will after exiting theinfluent channel 40 continue around 180 degrees inside of the bottomJ-shaped baffle 70 (see arrow 100 in FIGS. 1 and 3), plus an arc inwhich the inner radius transitions with the baffle straight portion 80.Thus the grit within the fluid will be forced toward the center and thestorage chamber 14, with the maximum radial distance for the grit totravel to the storage chamber 14 reduced by R_(d) (i.e., from inside theJ-shaped baffle 70 rather than from the storage chamber outer wall).

It should also be appreciated that the combination of both J-shapedbaffles 70, 72 with the ring 50 can further ensure that fluid enteringthe separation chamber 12 will travel around the chamber 12 at leastonce to provide efficient separation. This is particularly so inconfigurations in which the baffle curved portions 90, 92 extend farenough so that their ends 110, 112 distal from the straight portions 80,82 are substantially aligned or overlap such as best illustrated inFIGS. 2 and 3 (e.g., the exit from the influent channel 40 mayadvantageously be beneath or beyond the entrance to the effluent channel60. It should be appreciated that the exit from the influent channel 40into the separation chamber 12 is substantially aligned beneath theeffluent channel 60 such that any influent would have to flowessentially at least 360 degrees around the chamber before being able toenter the effluent channel 60.

It should be understood also that the straight portions 80, 82 could beoriented in different relative positions than illustrated in FIGS. 1-3(wherein they are substantially in line with one another). For example,baffle(s) according to at least one aspect of the present inventioncould be used if the environment of the apparatus 10′ requires that theeffluent flow back in the direction from which the influent came asshown in FIG. 6, or the apparatus 10″ requires influent and effluentflow at right angles as shown in FIG. 7. As with the FIGS. 1-4embodiment, the ends of the baffles could also be aligned, or overlap,or fall short of each other (i.e., the exit from the influent channel 40could end beneath the ring 50 before the entrance to the effluentchannel 60 above the ring 50, where the ring 50 is sufficient to blockflow from occurring straight from the influent channel outlet into theeffluent channel inlet), depending on the choice of arc from 90 to 270degrees of the baffle curved portions 90, 92. In such configurations thebaffle(s) may similarly advantageously improve efficiency by reducingthe maximum radial distance grit may be required to be separated intothe storage chamber 14, and may further advantageously assist inpreventing any influent from immediately and undesirably entering theeffluent channel 60 without flowing around entirely around the inside ofthe chamber at least once.

Still other aspects and advantages of the present invention may beobtained from a study of the disclosure herein.

1. A grit removal unit for a wastewater system, comprising: a round gritremoval chamber defined by a substantially horizontal bottom surface anda substantially annular vertical wall extending up from said bottomsurface; a substantially horizontal annular ring spaced above saidchamber bottom surface and extending inwardly from the chamber annularvertical wall to an inner edge, said ring extending around the entiretyof the chamber annular vertical wall; and an enclosed influent channelextending into said chamber beneath the ring, said influent channelhaving an outer side wall with a planar portion tangent to said chamberannular vertical wall and an inner side wall with a planar portion and acurved portion extending through an arc of at least about 90 degreeswithin said chamber annular vertical wall, wherein said inner side wallcurved portion extends downwardly from the inner edge of the ring to thechamber bottom surface.
 2. The grit removal unit of claim 1, whereinsaid inner side wall is a S-shaped baffle having a leg and a curvedportion extending at least about 90 degrees and concentric with saidchamber substantially annular vertical wall, with said J-shaped bafflecurved portion secured to the inner edge of said ring.
 3. The gritremoval unit of claim 2, wherein said J-shaped baffle curved portionspirals from a proximate end adjacent said J-shaped baffle leg to adistal end spaced from said J-shaped baffle leg, said spiral of saidJ-shaped baffle curved portion having a radius at said distal end whichis less than the radius at the proximate end.
 4. The grit removal unitof claim 1, wherein said enclosed influent channel inner side wallcurved portion extends through an arc of between about 90 degrees toabout 270 degrees within the chamber annular vertical wall.
 5. The gritremoval unit of claim 1, further comprising an effluent opening throughsaid removal chamber annular vertical wall and above said ring, whereinsaid influent channel has an outlet at the end of said inner side walland located sufficiently around said removal chamber to substantiallyprevent influent from said influent channel outlet exiting to saideffluent channel input without first entirely circling said chamber. 6.A grit removal unit for a wastewater system, comprising: a round gritremoval chamber defined by a bottom surface and a substantially annularvertical wall extending up from said bottom surface; a substantiallyhorizontal annular ring extending inwardly from the chambersubstantially annular vertical wall to an inner edge having a radiusR_(i), said ring being spaced above said chamber bottom surface andextending around the entirety of the chamber annular vertical wall; aninfluent channel through an opening in said chamber substantiallyannular vertical wall beneath said ring, said influent channel havingone influent side wall substantially tangential to said chambersubstantially annular vertical wall at said influent channel opening insaid chamber substantially annular vertical wall, and an influent innerside wall having a substantially flat portion parallel to said oneinfluent side wall and a curved portion extending between the chamberbottom surface and the ring, said influent inner side wall curvedportion having said radius R_(i) and extending through an arc of atleast about 90 degrees. said influent channel having an outlet at an endof the influent inner side wall curved portion.
 7. The grit removal unitof claim 6, wherein said inner side wall is a J-shaped baffle having aleg and a curved portion extending at least about 90 degrees andconcentric with said chamber substantially annular vertical wall, withsaid J-shaped baffle curved portion secured to the inner edge of saidring.
 8. The grit removal unit of claim 7, wherein said J-shaped bafflecurved portion spirals from a proximate end adjacent said J-shapedbaffle leg to a distal end spaced from said J-shaped baffle leg, saidspiral of said J-shaped baffle curved portion having a radius at saiddistal end which is less than the radius at the proximate end.
 9. Thegrit removal unit of claim 6, wherein said enclosed influent channelinner side wall curved portion extends through an arc of between about90 degrees to about 270 degrees within the chamber annular verticalwall.
 10. The grit removal unit of claim 6, further comprising aneffluent opening through said removal chamber annular vertical wall andabove said ring, wherein said influent channel has an outlet at the endof said inner side wall and located sufficiently around said removalchamber to substantially prevent influent from said influent channeloutlet exiting to said effluent channel input without first entirelycircling said chamber.
 11. A grit removal unit for a wastewater system,comprising: a round grit removal chamber defined by a bottom surface anda vertical wall substantially annular about a center and extending upfrom said bottom surface, said chamber vertical wall having a radius ofR_(VW) around a chamber center; a substantially horizontal annular ringextending inwardly a radial distance R_(d) from the chamber verticalwall, said ring being above said chamber bottom surface and extendingaround the entirety of the chamber annular vertical wall; an influentchannel through an opening in said chamber vertical wall and beneathsaid ring, said influent channel having a first influent side wallsubstantially tangential to said chamber vertical wall at said influentchannel opening in said chamber vertical wall, a second influent sidewall substantially parallel to said one influent side wall and spacedfrom said one influent side wall by said distance R_(d), and a curvedextension of said second influent side wall within said chamber, saidcurved extension having a radius of R_(ex), wherein R_(ex)=R_(VW)−R_(d),and said second influent side wall and curved extension extend from saidchamber bottom surface to said ring wherein said influent channel isdefined between said first and second influent side walls, said curvedextension, said ring, and said chamber bottom surface; and an effluentopening through said chamber vertical wall and above said ring, whereinsaid influent channel has an outlet at the end of said inner side walland located sufficiently around said removal chamber to substantiallyprevent influent from said influent channel outlet exiting to saideffluent channel input without first entirely circling said chamber;wherein said curved extension of said influent channel second side wallextends through an arc of at least about 90 degrees around said center.12. The grit removal unit of claim 11, wherein said inner side wall is aJ-shaped baffle having a leg and a curved portion extending at leastabout 90 degrees and concentric with said chamber substantially annularvertical wall, with said J-shaped baffle curved portion secured to theinner edge of said ring.
 13. The grit removal unit of claim 12, whereinsaid J-shaped baffle curved portion spirals to a distal end spaced fromsaid J-shaped baffle leg, said spiral of said J-shaped baffle curvedportion having a radius at said distal end which is greater than R_(ex).14. The grit removal unit of claim 11, wherein said enclosed influentchannel inner side wall curved portion extends through an arc of betweenabout 90 degrees to about 270 degrees within the chamber annularvertical wall.